Understanding the Functional Roles of Newly Identified Serine `Orphan' Proteases and Two Chymotrypsins in the Aedes aegypti Midgut Project Summary/Abstract The female Aedes aegypti mosquito completely relies on human blood as its main source of nutrients. A single female Ae. aegypti mosquito can lay up to 200 eggs from a single blood meal, and the digestion process is highly dependent on midgut proteolytic enzymes. In vivo studies of four abundant midgut proteases have revealed the importance of only three on maximal fecundity. However, RNAi knockdown studies of all three at once did not have an overall synergistic effect indicating the involvement of other midgut proteases. Indeed, mRNA transcripts of five new serine 'orphan' proteases have been identified, but their physiological roles in this process have not been studied in vivo or in vitro making it unknown how much they contribute to overall fecundity. In addition, the exact role in digestion and overall fecundity of two chymotrypsin-like proteases remains unclear. We hypothesize that the orphan proteolytic and the chymotrypsin-like enzymes play important functional roles in the blood meal digestion process. Because the functions of these proteases are novel in mosquitoes, they will bear broadly on the study of a crucial model organism in vector biology. This proposal will focus on elucidating the physiological roles of these serine proteases using RNAi technology, in vivo and in vitro midgut proteolytic activity assays, fecundity studies (Aim 1), recombinant protein expression and purification for in vitro kinetic and substrate specificity assays, as well as mutational and structural determination using crystallography (Aim 2). Overall, the work will lead to complete understanding of the role and specificity of all known mosquito midgut proteases in the blood meal digestion process and may lead to the development of a potential novel mosquito (vector) control strategy. This is crucial because the mosquito is able to transmit several viral pathogens during blood feeding, and if blood meal digestion is interrupted, the mosquito will not lay eggs minimizing the mosquito population, and in turn minimize pathogen transmission. Furthermore, the information gained from this work may be applied to other vector mosquito species and other blood feeding insect vectors that heavily rely on midgut proteolytic enzymes for digestion.